The present invention relates to a low cost air loss mattress assembly adapted for use with standard hospital bed frames and residential beds for the prevention and treatment of decubitus ulcers, also known as pressure sores or bed sores. While various mattress and bed assemblies have been previously developed and used for patients with decubitus ulcers or at decubitus risk, they generally require specially fabricated bed frames or extensive modifications to existing frames, are very costly, cumbersome, and extremely heavy, all of which have greatly restricted their availability and use. In addition, such devices often fail to satisfy all of the necessary needs which must be met to successfully prevent or treat decubitus ulcers.
Decubitus ulcers result from excessive force and pressure upon the skin over a prolonged period of time, and typically occur on bedridden patients who are limited partially or totally in their mobility. Such immobility occludes blood and interstitial fluid transport by prolonging pressure on the dermis, often at bony protuberances, which exceeds the pressure necessary to close capillaries. While exceeding such pressure for short periods of time is a routine and safe occurrence for active individuals, prolonged capillary closure reduces the oxygenation of tissues to a level that causes cell death in the underlying tissue, creating a decubitus ulcer.
The pressure on the skin necessary to effect capillary closure typically is only 32 mm. Hg. An average person of 150 pounds sitting in a chair, assuming even distribution of the load, generates a pressure of about 54 mm. Hg. on the skin in the buttock/thigh support area. Accordingly, it is almost physically impossible to support a typical adult in a seated position without exceeding the capillary closure pressure, because there is insufficient surface over which to distribute the load. However, a patient lying horizontally has enough surface area to distribute the load without generating peak pressures in excess of 32 mm. Hg., if the support surface is appropriately designed.
In addition to providing such low contact pressure in the prevention and treatment of decubitus ulcers, it is necessary to prevent skin maceration, to reduce the shear forces exerted by the support surface on the skin, and to prevent temperature extremes on the skin, as these conditions also contribute to the formation and worsening of decubitus ulcers. Conventional hospital bedding fails on all counts. It cannot accommodate a topographic prominence (bony protuberance) by deforming adequately at the site of the load and thus does not sufficiently distribute the load from the prominence to the surrounding region. High pressures at the prominence result, creating a severe risk of decubitus ulceration. The water impermeable bacteriocidal covers used on conventional hospital mattresses are not only inelastic, creating an excessive pressure buildup on bony protuberances, but hold moisture such as perspiration and urine in contact with the skin, which macerates and weakens the skin. Bacteriocidal covers may also trap heat and cause elevated skin temperature. Macerated skin is highly susceptible to damage from the shear forces which result when a person moves, is pulled across a bed surface, or when the person's bed pan, dressings or clothing is changed. Further, bacteria and viruses are harbored in the moisture held against the skin by these nonporous covers. Preventing or inhibiting normal evaporation of perspiration precludes normal cooling of the skin. When the dead or macerated skin is ruptured by the rubbing movement of the patient against the mattress or sheet or where the skin is already breached, the bacteria and viruses are able to enter the ruptured skin and cause local as well as systemic infections. Conventional mattress and bedding designs do not adequately reduce these shear forces. The coefficient of friction against skin of ordinary cotton or cotton/polyester sheets is sufficient to easily injure macerated skin.
Minimal skin contact pressure, moisture control, reduced shear forces and in some cases temperature control, must be provided in a mattress assembly which can effectively prevent and treat decubitus ulcers. For such an assembly to be readily accessible to the majority of patients at risk for decubitus ulcers or with existing decubitus ulcers, it is important that such a mattress assembly be relatively inexpensive, not unduly cumbersome or heavy, easily operable and adjustable and retrofitable to standard hospital bed frames and residential beds without extensive modification. While conventional hospital beds are readily accessible, they fail to meet the basic needs necessary to prevent or treat decubitus ulcers. A number of therapeutic beds have heretofore been developed to replace the standard hospital bed for such prevention or treatment. While some of those beds do provide reduced skin contact pressure and some provide somewhat improved moisture control under certain limited circumstances, they generally fail to address the problem of shear force, are very expensive, and cannot be readily retrofitted to standard hospital bed frames or residential beds. In addition, many are very cumbersome and extremely heavy, sometimes exceeding floor loading limits in some hospitals and in most nursing and residential homes as well as creating storage problems. Many of the therapeutic beds heretofore developed also create significant cleaning and/or sterilization problems, and often require an experienced technician to install, operate and adjust the beds properly to meet the patient's needs. Many of the beds can not meet several needs simultaneously, because the solution for one often defeats the effectiveness for others. As a result, access to such beds has been very limited, and decubitus ulcers continue to be a substantial problem with bedridden patients.
The mattress assembly of the present invention simultaneously fulfills each of the requirements necessary to prevent and treat decubitus ulcers. It provides the necessary support to maintain the contact pressure with the skin at a level below 32 mm. Hg., avoiding capillary closure and cell death in the skin and underlying tissue, the primary cause of decubitus ulcers. It draws moisture away from the skin, while directing a selective air flow through the mattress surface to the skin to maintain the skin in a properly hydrated condition, and significantly lowers the coefficient of friction between the skin and the mattress to reduce the damaging shear forces exerted on the skin. It also readily accommodates temperature control of the bed surface. The mattress assembly disclosed herein does not require a special bed frame, but can be readily retrofitted to existing hospital bed frames and residential beds, significantly reducing the cost of decubitus treatment and prevention, while substantially increasing its availability to those in need.
Much of the present mattress assembly can also be made disposable, obviating the need for repeated cleaning and sterilization and thus greatly reducing the chance of contaminating other patients as well as reducing the costs associated therewith. This later feature is of particular significance in treating persons afflicted with Acquired Immune Deficiency Syndrome. Further, much of the mattress assembly can also be easily cleaned while in service, can be laundered locally, or could be reprocessed in a centralized cleaning/repackaging facility when reuse is preferable to disposal. In addition to the treatment and prevention of decubitus ulcers, the mattress assembly disclosed herein is very useful for treating patients with burns, wounds, incisions, and other conditions of the skin and/or underlying tissue.